Consumers have developed an unrestrained desire for smart "daily aids" in all areas of life. The spectrum ranges from smart speakers through controlling their smart home to vehicles equipped with more and more virtual assistants. This trend can also be observed in the textile sector. The expectations placed on a textile have changed and the increased requirements demand intelligent solutions. Consumers today expect multifunctionality, e.g. they want to be able to communicate with the help of textiles. Such smart textiles are realized through specifically integrated electronics. According to forecasts by IDTechEx, the global market for smart textiles will be worth about US$ 1.3 billion by 2031. The pre-requisite, therefore, is an efficient combination of textiles and electronics which offers sufficient technological flexibility for different application scenarios – from body-hugging clothing or medical textiles to architectural elements.
A distinction can be made between passive and active smart textiles. Passive smart textiles can only perceive their environment via sensors, whereas active smart textiles can also react to external actions. Conventional textiles can be upgraded by further developments that focus on combining new materials and technologies to create new application possibilities. Smart textiles technology combines classic textile products with ultra-modern electronic applications. If this high-tech upgrading of textiles takes place via embroidery technology, conductive materials are applied to the embroidery base instead of typical embroidery materials. Embroidery technology offers numerous advantages over other textile technologies because components can be freely positioned on the embroidery ground, which allows individual patterns and structures. There are various approaches possible in the spectrum from textile-integrated and textile-adapted to textile-based smart textiles.
Textile-integrated – reliable but inflexible
The approach of textile-integrated smart textiles allows the use of standard electronic components, e.g. wire material. With the help of soutache technology not only cords, fancy yarns or ribbons, but also functional, textile-untypical thread-like longitudinal structures such as wire strands or sheathed wires can be applied. These are reliable in their function. However, the disadvantage is that the textile properties are often lost due to the material stiffness and the material is less resistant to kinking. Despite this challenge, this technology is already being used in the industrial production of car seat heaters. However, other areas of application in which the flexibility of the textile plays a subordinate role are also possible.
An example of the use of this technology is provided by Bionic RoboSkin, a current research project at the Textilforschungsinstitut Thüringen-Vogtland e.V. (TITV), Greiz/Germany (BMBF, 16ES0910K). It is concerned with the development of a robust sensor skin for service robots to be used under water. The project is pursuing the approach of using textile carriers as an integration platform. The integration of the necessary sensor elements into the textile carrier substrate is primarily carried out using embroidery technology. For the realization of the envisaged sensor skin, saltwater-resistant wire material is applied to the textile carrier in different shapes and distances using the soutache technology (Fig. 1). Users of robot systems for underwater service or geo-exploration can therefore look forward to the support of robots with textile-based sensor technology in the near future.
Textile-adapted – elaborate development for more flexibility
Embroidery is an established technology for the production of smart textiles in the textile-adapted approach, as it enables not only the integration of wire materials but also the incorporation of standardized electrical components into textile substrates. In this process, complex components are contacted with the conductor paths with the help of conductive thread material. The thread material connects the embroidery base to the components via the metallized openings provided in the component. The shape and design of these openings must firstly be adapted to the special features of the stitching process, whereby the geometry and placement of the openings must take into account the technical embroidery requirements. The challenging aspect of the machine processing of the components is that they must not be damaged during the embroidery process. The settings on the stitch-forming elements have to be adjusted so that a smooth embroidery process can take place. The complex development of the components and the required precision in processing are only economical for products that have to be flexible and resistant to buckling due to the area of application, or that have to offer complex functionalities through various electronic components. Due to the lengthy and cost-intensive development of textile-adapted electronic components, the resulting smart-textile products must either be offered at a high price on the market or be produced in large quantities in a standardized and automated manner in order to reduce the product price through scaling effects.
Fig. 2: Contacting of electronic components using embroidery technology (Source: TITV Greiz)
In the Textile Prototyping Lab research project (BMBF, 03ZZ0650D), the TITV Greiz uses embroidery technology to incorporate the components developed by Fraunhofer IZM into the textile. The TITV Greiz has succeeded in processing these electronic elements from this modular system on a laboratory scale using embroidery machines from industry (Fig. 2).
Textile-based – invisible electronics
A very good textile-processability, while maintaining the textile character, is pursued with the approach of textile-based smart textiles. The reliability of the function in particular is still a major challenge during its development. Nonetheless, successful work is increasingly being done here so that a visual upgrade of the prototypes significantly supports a sustainable market launch.
Fig. 3: Embroidered electrodes (Source: TITV Greiz)
Embroideries have been familiar to consumers for centuries. They surround people in everyday home fashion and are encountered in their wardrobes. This familiarity also supports the establishment of embroidered medical products on the market. Using this technology, which was once used as an ornament, it is possible to produce electrodes close to the body for recording various vital parameters by processing conductive functionalized thread material (Fig. 3). Here, the visual appearance can bring decisive advantages in terms of acceptance. Embroidered textiles are familiar to us and can convey confidence in the technology more quickly than non-textile competitor products made of materials that users naturally do not want to wear directly on their bodies. The research project iTex-4-MoRe – Intelligent Textiles for Physiotherapy in Mobile Rehabilitation (AiF IGF 21117 BR/2) aims to develop comfortable sensor technology. Textile-based EMG (electromyography) electrodes are used to measure muscle activity. Until now, surface or needle electrodes have been necessary for this, which have to be positioned professionally on the skin or in the muscle. Particularly in the case of necessary medical examinations close to the body, textile-based medical products can more readily overcome the associated obstacles, for example, in children.
Depending on the desired application, the advantages and disadvantages of the processing principles must be weighed up in terms of reliability, functionality, comfort and economy. However, all approaches have one thing in common. They show the versatile possibilities of embroidery technology for the development and production of smart textiles.
The authors thank the BMBF, BMWi of the AiF for the financial support.
Textilforschungsinstitut Thüringen-Vogtland e.V. (TITV), Greiz/Germany